Fan coil thermostat with fan ramping

ABSTRACT

Fan coil thermostats can provide energy savings by, for example, operating a fan coil system more efficiently. Fan coil systems employing such a fan coil thermostat may be more energy efficient. A fan coil system may include a fan coil that is configured for fluid communication with a source of heated fluid and/or a source of cooled fluid, a valve that controls fluid flow through the fan coil and a fan that blows air across the fan coil. The fan coil thermostat may include a controller that implements a control algorithm that calculates an error percentage value relating to a temperature difference between the current temperature and the temperature set point. The error percentage value may include a proportional term related to the temperature difference and an integral term related to the temperature difference. The controller may regulate the fan speed in accordance with the calculated error percentage.

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/740,789, filed Jun. 16, 2015, entitled “Fan Coil Thermostatwith Fan Ramping”, which is a continuation of co-pending U.S. patentapplication Ser. No. 11/833,703, filed Aug. 3, 2007, entitled “Fan CoilThermostat with Fan Ramping”, now U.S. Pat. No. 9,074,784, issued Jul.7, 2015, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains generally to thermostats and moreparticularly to thermostats adapted for use with fan coils.

BACKGROUND

A variety of buildings such as hotels, apartment buildings and the likeare heated and cooled using fan coil systems. In a fan coil system, aheat transfer fluid such as water is pumped or otherwise forced througha fan coil. A fan is used to blow air across the fan coil. If the heattransfer fluid was heated, heated air will blow out of the fan coilsystem. Conversely, if the heat transfer fluid was cooled, cool air willblow out of the fan coil system.

Like other HVAC systems, fan coil systems often consume significantamounts of energy. A significant amount of energy may be saved, forexample, by operating fan coil systems more efficiently.

SUMMARY

The present disclosure pertains to fan coil thermostats that can provideenergy savings and or increased comfort by, for example, operating a fancoil system more efficiently.

In an illustrative but non-limiting example, a fan coil thermostat isconfigured for use with a fan coil system. In some cases, the fan coilsystem includes a fan coil that is configured for fluid communicationwith a source of heated fluid and/or a source of cooled fluid, a valvethat controls fluid flow through the fan coil, and a fan that blows airacross the fan coil.

The fan coil thermostat may include a user interface that is adapted topermit a user to enter a temperature set point. The fan coil thermostatmay include or be in communication with a temperature sensor that isadapted to measure a current ambient temperature. The fan coilthermostat may include a controller that is adapted to implement acontrol algorithm for controlling the fan coil system. In some cases,the control algorithm calculates an error value relating to atemperature difference between the current sensed temperature and thecurrent temperature set point. To operate the fan coil system moreefficiently and/or with increased comfort, the control algorithm may useboth a proportional term and an integral term related to the error valueto regulate the fan speed of the fan coil system.

The above summary is not intended to describe each disclosed embodimentor every implementation of the present invention. The Figures andDetailed Description that follow more particularly exemplify theseembodiments.

BRIEF DESCRIPTION OF THE FIGURES

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of an illustrative but non-limiting fan coilsystem;

FIG. 2 is a schematic view of an illustrative but non-limiting fan coilthermostat as may be used in the fan coil system of FIG. 1;

FIG. 3 is a front view of an illustrative embodiment of the fan coilthermostat of FIG. 2;

FIG. 4 is a block diagram showing an illustrative control algorithm thatmay be employed within the fan coil system of FIG. 1;

FIG. 5 is a flow diagram showing an illustrative method that may becarried out using the fan coil system of FIG. 1; and

FIG. 6 is a flow diagram showing an illustrative method that may becarried out using the fan coil system of FIG. 1.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular illustrative embodiments described. On the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention.

DETAILED DESCRIPTION

The following description should be read with reference to the drawings,in which like elements in different drawings are numbered in likefashion. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Although examples of construction, dimensions, and materialsmay be illustrated for the various elements, those skilled in the artwill recognize that many of the examples provided have suitablealternatives that may be utilized.

FIG. 1 is a schematic view of an illustrative but non-limiting fan coilsystem 10. While the illustrative fan coil system 10 is schematicallyshown as a two-pipe fan coil system including a single supply line and asingle return line, it will be appreciated that fan coil system 10 mayinstead be a four-pipe fan coil system having heated water supply andreturn lines as well as cooled water supply and return lines. In somecases, a four-pipe system may include a single fan coil while in othercases, a four-pipe system may include two fan coils, with one dedicatedto heated and one dedicated to cooling. In a two-pipe fan coil system,the single supply line may, for example, provide heated water during theheating season and may provide cooled water during the cooling season.

The illustrative fan coil system 10 includes a fan coil 12. Fan coil 12is a heat exchanger through which heated or cooled fluid flows. A fan 14blows air across fan coil 12 as schematically shown by arrows 16. Insome cases, fan 14 pulls ambient air from within the space and/or fromoutside the building. The ambient air is then heated or cooled by thefan coil 12 and provided into the space. In some cases, fan coil system10 may be disposed within a housing (not shown) having a first vent oropening upstream of fan 14 and a second vent or opening downstream offan coil 12. Fan 14 may pull air through the first vent or opening andthen exhaust the heated or cooled air through the second vent or openingand into the space. The components may be arranged either horizontallyor vertically within such a housing, as desired or perhaps as dictatedby space considerations.

In order to accommodate fluid flow through fan coil 12, fan coil system10 includes a supply line 18 and a return line 20. During the heatingseason, supply line 18 provides a source of heated fluid (such as water)from a suitable source such as a boiler or water heater, geothermaland/or the like. During the cooling season, supply line 18 provides asource of cooled fluid (such as water) from a suitable source such as anevaporative cooling tower or the like.

A valve 22 is disposed within supply line 18, upstream of fan coil 12,in order to control fluid flow through fan coil 12. In some cases, valve22 may provide binary, i.e., on/off control while in other cases it iscontemplated that valve 22 may be configured to provide a plurality offlow rates into fan coil 12.

Fan coil system 10 may include a fan coil thermostat 24 that controlsoperation of valve 22 and/or operation of fan 14 in order to achieve adesired temperature level within a space that is conditioned by fan coilsystem 10. Fan coil thermostat 24 is better described with respect toFIG. 2. FIG. 2 schematically shows various components of an illustrativefan coil thermostat 24. The illustrative fan coil thermostat 24 includesa user interface 26 that may include a display 28 and a keypad 30.Display 28 may be any suitable alphanumeric display medium that iscapable of displaying visually discernible information. In some cases,display 28 may be a liquid crystal display (LCD), but this is notrequired. Keypad 30 may include one or more individual electromechanicalbuttons such as such as an on/off button, a temperature up button, atemperature down button, a fan speed up button, a fan speed down button,and the like. In some cases, it is contemplated that user interface 26may be a touch screen LCD that encompasses the function of display 28 aswell as keypad 30. That is, the buttons of keypad 30 may include, forexample, electromechanical buttons, soft buttons, and/or touch regionson a touch screen display, as desired.

The illustrative fan coil thermostat 24 may include a controller 32. Insome cases, controller 32 may implement a control algorithm that isadapted to at least partially control one or more components of fan coilsystem 10. In some instances, the control algorithm may control and/orregulate operation of fan 14 (FIG. 1).

In some cases, the control algorithm may determine fan speed based atleast in part on if valve 22 (FIG. 1) is open or closed and/or how farvalve 22 is open. In some instances, the control algorithm may dictatethat fan 14 (FIG. 1) is off if valve 22 is closed. As valve 22 opens,the control algorithm may dictate that fan 14 is running at, forexample, a low speed, a medium speed, a high speed or the like. In somecases, the control algorithm may determine a fan speed also based atleast in part on a temperature differential between a current sensedtemperature and a current temperature set point, and/or a current sensedhumidity and a current humidity set point.

Controller 32 may be adapted to provide information to and/or receiveinformation from user interface 26. Controller 32 may, for example,display a current temperature and/or a current temperature set point ondisplay 28. Other examples of information that may be provided bycontroller 32 include a current fan speed, current fan mode, equipmentstatus (on/off), current time, and the like. Examples of informationthat may be received from keypad 30 may include changes in a temperatureset point, changes in fan speed and the like.

In some cases, the illustrative fan coil thermostat 24 may include amemory block 34. Memory block 34 may be used, for example, to store oneor more unoccupied temperature set points, a current temperature setpoint, and/or programming that instructs controller 32 how to regulatevalve 22 (FIG. 1) and/or fan 14 (FIG. 1) in order to obtain and maintaina particular temperature set point. Memory block 34 may store, forexample, the aforementioned control algorithm.

In some instances, fan coil thermostat 24 may include a sensor 36 thatprovides controller 32 with information pertaining to current conditionswithin a space conditioned by fan coil system 10 (FIG. 1). Sensor 36 maybe a temperature sensor, a humidity sensor and/or any other suitablesensor, as desired. In some cases, sensor 36 may be located internallyto fan coil thermostat 24, although in some instances, sensor 36 mayinstead be located remotely from fan coil thermostat 24.

FIG. 3 is a front view of an illustrative fan coil thermostat 40. Fancoil thermostat 40 may be considered as an embodiment or perhaps as aparticular example of fan coil thermostat 24 (FIG. 2). The illustrativefan coil thermostat 40 includes a housing 42 that may be formed of anysuitable material such as molded plastic. The illustrative fan coilthermostat 40 also includes a display 44 that may be any suitabledisplay such as an LCD display.

The illustrative fan coil thermostat 40 also includes several buttonsthat may be considered as examples of keypad 30 (FIG. 2). The buttonsillustrated are not to be considered as limiting in any way, but aremerely provided to show examples of buttons that may be included. Asillustrated, fan coil thermostat 40 includes a fan speed up button 46and a fan speed down button 48. In some cases, it is contemplated thatfan coil thermostat 40 may include a single fan speed button (not shown)that can be pressed repeatedly to step through the available fan speedsettings. In some instances, a slider button or even a rotary dial maybe provided to select a fan speed setting.

As illustrated, fan coil thermostat 40 includes a temperature up button50 and a temperature down button 52. A user may select and/or alter atemperature setting by pressing temperature up button 50 and/ortemperature down button 52, as appropriate. A power button 54 may alsobe provided. It is contemplated that fan coil thermostat 40 may insteadhave a touch screen LCD that provides the functionality of display 44 aswell as fan speed up button 46, fan speed down button 48, temperature upbutton 50, temperature down button 52, and power button 54. In somecases, the various buttons may be provided as touch regions on the touchscreen display.

FIG. 4 is a block diagram of an illustrative control algorithm forcontrolling the fan speed of the fan coil thermostat 24. In generalterms, the illustrative control algorithm compares the currenttemperature set point to the current temperature reading provided bytemperature sensor 36 (FIG. 2), and then calculates therefrom an errorpercentage 70. The error percentage 70 is calculated using both aproportional term 66 and an integral term 64, as shown. The resultingerror percentage 70 is then used to select a suitable fan speed foroperating fan 14 (FIG. 1), as will be discussed subsequently.

For the purposes of this discussion, the error percentage 70 may beconsidered as representative of a temperature difference between atemperature set point and a current temperature reading relative to athrottling range (or gain). The throttling range is a parameter that maybe set when programming controller 32 and may be considered asrepresenting a temperature difference at which controller 32 wouldinstruct fan coil system 10 (FIG. 1) to operate at maximum output.

To illustrate, assume for a moment that the throttling range has beenset equal to 5° F. If a temperature difference is 5° F., the errorpercentage would be 100%. If the temperature difference is 2° F., theerror percentage would be 40%. It will be recognized that the throttlingrange is a parameter that depends at least in part upon systemparticulars and system performance parameters and thus the numericalexamples provided herein are merely illustrative and should not beconstrued or interpreted as limiting in any manner. One of skill in theart will recognize that the block diagram provided in FIG. 4 illustratesan inventive application of P-I (proportional-integral) control to a fancoil thermostat, thereby providing improved fan control and thusimproved energy efficiency, consumer comfort and the like.

Referring specifically to FIG. 4, and at block 56, controller 32 (FIG.2) receives a signal from user interface 26 (FIG. 1) and/or from memory34 (FIG. 2) that represents a current temperature set point. Block 58represents controller 32 receiving a signal representing a currenttemperature reading from, for example, sensor 36 (FIG. 2). The signalfrom block 56 and the signal from block 58 are summed (or subtracted) atsummation point 60 to provide a signal representing an error indicatedas (Err) 62.

Signal (Err) 62 is provided to block 64 as well as to block 66. At block64, controller 32 (FIG. 2) effectively integrates the (Err) signal 62.In the given equation, K_(p) is the gain (or 100%/throttling range) andTi is an integral time constant. At block 66, controller 32 alsocalculates a proportional contribution, using a gain of K_(p). Theresultant values are summed at summation block 68 to provide the errorpercentage 70.

The error percentage 70 enters a fan speed driver 72, which in somecases may be considered as manifested within the programming ofcontroller 32. In some cases, controller 32 may not instruct fan 14 tooperate at all, if for example valve 22 (FIG. 1) is closed, regardlessof whether error percentage 70 would otherwise indicate a non-zero fanspeed. As can be seen, if error percentage 70 is between 0 and a firstthreshold, controller 32 may instruct fan 14 (FIG. 1) to operate at alow fan speed.

If error percentage 70 is above the first threshold but below a secondthreshold, controller 32 may instruct fan 14 to operate at a medium fanspeed. If error percentage 70 is above the second threshold, controller32 may instruct fan 14 to operate at a high fan speed.

While FIG. 4 pertains to a fan 14 (FIG. 1) that has a low fan speed, amedium fan speed and a high speed, it will be recognized that in somecases, fan 14 may have more than three distinct speeds, or may in somecases have fewer than three distinct speeds. In some instances, fan 14may have an infinite number of fan speeds. In any event, fan speeddriver 72 may be adjusted or altered to compensate for a differentnumber of speeds.

In some cases, error percentage 70 may be exactly or almost exactlyequal (within the precision of controller 32) to either the firstthreshold or the second threshold. In some cases, the low fan speed mayapply if error percentage 70 is less than or equal to the firstthreshold while in other cases, the low fan speed may apply only iferror percentage 70 is less than the first threshold. Similarly, themedium fan speed may apply if error percentage 70 is less than or equalto the second threshold, while in some cases the medium fan speed mayonly apply if error percentage 70 is less than the second threshold. Inother words, whether a particular threshold is regarded as “equal to orless than” or only “less than” is merely a programming matter. Moreover,it is contemplated that fan speed driver 72 may provide a degree ofhysteresis when switching between low, medium and high fan speeds. Forexample, and in some cases, when switching between the low fan speed andthe medium fan speed, the error percentage 70 may need to exceed thefirst threshold by a certain amount, and when switching between themedium fan speed and the low fan speed, the error percentage 70 may needto drop below the first threshold by a certain amount. The same may beapplied when switching between the medium fan speed and the high fanspeed. Such hysteresis may help reduce short term switching of the fanspeed when the error percentage 70 is at or near the first and/or secondthresholds.

The first threshold and the second threshold may be set equal to anydesired value. In an illustrative but non-limiting example, the firstthreshold may be set equal to about 40% and the second threshold may beset equal to about 80%. It will be appreciated that other values may beused, and thus the control algorithm may be fine-tuned for a particularapplication.

FIG. 5 shows an illustrative method that may be carried out using fancoil system 10 (FIG. 1). At block 74, controller 32 (FIG. 2) obtains acurrent temperature value from sensor 36 (FIG. 2). Control passes toblock 76, where controller 32 compares the current temperature valuewith a temperature set point that may be received from user interface 26(FIG. 2) and/or from memory block 34 (FIG. 2) to determine a temperaturedifference. At block 78, an error percentage is calculated. The errorpercentage includes a contribution that is made by integrating thetemperature difference. In some cases, as seen at block 80, there mayalso be a contribution that is proportional to the temperaturedifference.

Control passes to block 82, where controller 32 (FIG. 2) selects a fanspeed based on the error percentage value. In some cases, a low fanspeed may be selected if the error percentage value is below a firstthreshold. A medium fan speed may be selected if the error percentagevalue is above the first threshold but below a second threshold. A highfan speed may be selected if the error percentage value is above thesecond threshold. At block 84, controller 32 operates fan 14 (FIG. 1) inaccordance with the selected fan speed.

FIG. 6 shows an illustrative method that may be carried out using fancoil system 10 (FIG. 1). At block 74, controller 32 (FIG. 2) obtains acurrent temperature value from sensor 36 (FIG. 2) and compares it to atemperature set point (at block 76) to determine a temperaturedifference. At block 78, an error percentage is calculated. The errorpercentage includes a contribution that is made by integrating thetemperature difference. In some cases, as seen at block 80, there mayalso be a contribution that is proportional to the temperaturedifference.

Control passes to block 86, where controller 32 (FIG. 2) controls fluidflow through fan coil 12 (FIG. 1) by opening and/or closing valve 22(FIG. 1) in accordance with the temperature set point. At block 82,controller 32 (FIG. 2) selects a fan speed based on the error percentagevalue. In some cases, a low fan speed may be selected if the errorpercentage value is below a first threshold. A medium fan speed may beselected if the error percentage value is above the first threshold butbelow a second threshold. A high fan speed may be selected if the errorpercentage value is above the second threshold. At block 88, controller32 operates fan 14 (FIG. 1) in accordance with the selected fan speed iffluid is flowing through fan coil (12). In some cases, if no fluid isflowing through fan coil (12), fan (14) will not operate, regardless ofthe error percentage value.

While the present disclosure has been described with respect toillustrative fan coil systems that include one or more pipes carryingheated water for heating and/or cooled water for cooling, it should benoted that the inventive concepts described herein are not limited tosuch systems. Some systems may be hybrid-type systems, with an A/Ccompressor for cooling and heated water for heating. Some systems may bethrough-the-wall systems, having one or more of a compressor for airconditioning, an electric or gas heating element for heating, and a heatpump. Fan coil thermostat 40 may, for example, be used with thesesystems as well as the systems described herein.

The present disclosure should not be considered limited to theparticular examples described above, but rather should be understood tocover all aspects of the invention as fairly set out in the attachedclaims. Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

What is claimed is:
 1. A method of operating a fan coil systemcomprising a fan coil and a fan adapted to blow air across the fan coil,the fan having a plurality of fan speeds, the method comprising:displaying a temperature set point on a user interface, the temperatureset point being adjustable via the user interface; obtaining a currenttemperature value from a temperature sensor; determining a temperaturedifference between the current temperature value and the temperature setpoint; storing a maximum temperature difference, a first threshold forthe temperature difference that is less than the maximum temperaturedifference and a second threshold that is greater than the firstthreshold and less than the maximum temperature difference; establishinga fan throttle range based on the maximum temperature difference;operating the fan at a low fan speed within the fan throttle range whenthe temperature difference is below the first threshold; operating thefan at a medium fan speed within the fan throttle range when thetemperature difference is between the first threshold and the secondthreshold; and operating the fan at a high fan speed within the fanthrottle range when the temperature difference is above the secondthreshold.
 2. The method of claim 1, further comprising: implementinghysteresis when switching between the low fan speed and the medium fanspeed.
 3. The method of claim 1, further comprising: implementinghysteresis when switching between the medium fan speed and the high fanspeed.
 4. The method of claim 1, where the fan speed is controlled by acontroller that is programmed with a proportional-integral (PI) controlalgorithm.
 5. The method of claim 4, wherein the PI control algorithmcomprises a proportional term including the temperature difference(T_(ERR)) and a gain constant (Kp), and further comprising an integralterm including the temperature difference (T_(ERR)), a time constant(Ti) and the gain constant (Kp).
 6. The method of claim 5, wherein theproportional term is of the form Kp*T_(ERR), and the integral term is ofthe form: $\frac{K_{P}}{T_{i}}{\int_{0}^{t}{T_{ERR}{dt}}}$
 7. Themethod of claim 1, where the fan throttle range is established such thatthe fan operates at a maximum speed when the temperature differenceapproaches the maximum temperature difference.
 8. The method of claim 1,where the fan throttle range is established such that when thetemperature difference is less than 100% of the maximum temperaturedifference, the fan is operated at a corresponding percentage of amaximum fan speed.
 9. The method of claim 1, wherein the fan coilaccommodates fluid flow therethrough.
 10. A fan coil thermostat for usewith a fan coil system having a fan coil and a fan adapted to blow airacross the fan coil, comprising: a housing; a user interface disposed inthe housing and accessible from outside of the housing, the userinterface including at least one button for allowing a user to enter atemperature set point; a temperature sensor configured to measure acurrent temperature; a controller disposed within the housing andimplementing a fan speed control algorithm that calculates a controlerror based on a temperature difference between the current temperatureand the temperature set point, the control error extending from notemperature difference to a predefined maximum temperature difference;and the fan speed control algorithm correlating the control error to afan throttle range extending from a low fan speed to a medium fan speedto a high fan speed and selecting a fan speed based on the controlerror.
 11. The fan coil thermostat of claim 10, the control errorcomprising a proportional term including the temperature difference andan integral term including the temperature difference.
 12. The fan coilthermostat of claim 10, where the fan speed control algorithm comprisesa proportional-integral (PI) control algorithm.
 13. The fan coilthermostat of claim 12, wherein the PI control algorithm comprises aproportional term including the temperature difference (T_(ERR)) and again constant (Kp), and further comprises an integral term including thetemperature difference (T_(ERR)), a time constant (Ti) and the gainconstant (Kp).
 14. The fan coil thermostat of claim 13, wherein theproportional term is of the form Kp*T_(ERR), and the integral term is ofthe form: $\frac{K_{P}}{T_{i}}{\int_{0}^{t}{T_{ERR}{dt}}}$
 15. Thefan coil thermostat of claim 10, where the fan throttle range isestablished such that the fan operates at a maximum speed when thetemperature difference approaches the predefined maximum temperaturedifference.
 16. The fan coil thermostat of claim 10, where the fan speedcontrol algorithm implements hysteresis when switching between the lowfan speed and the medium fan speed.
 17. The fan coil thermostat of claim10, where the fan speed control algorithm implements hysteresis whenswitching between the medium fan speed and the high fan speed.
 18. Thefan coil thermostat of claim 10, where the fan speed control algorithmstores the predefined maximum temperature difference, a first thresholdfor the temperature difference that is less than the predefined maximumtemperature difference and a second threshold that is greater than thefirst threshold and less than the predefined maximum temperaturedifference.
 19. The fan coil thermostat of claim 18, where the fan speedcontrol algorithm operates the fan at a low fan speed within the fanthrottle range when the temperature difference is below the firstthreshold, operates the fan at a medium fan speed within the fanthrottle range when the temperature difference is between the firstthreshold and the second threshold, and operates the fan at the high fanspeed within the fan throttle range when the temperature difference isabove the second threshold.
 20. A method of operating a fan coil systemcomprising a fan coil and a fan adapted to blow air across the fan coil,the fan having a fan speed range, the method comprising: obtaining acurrent temperature value from a temperature sensor; storing a maximumtemperature difference; determining a current control error, the currentcontrol error representing a difference between the current temperaturevalue and a temperature set point over a control error range that isbounded by no temperature difference on one end to the maximumtemperature difference on the other end, and wherein the current controlerror is set to the maximum temperature difference if the differencebetween the current temperature value and the temperature set point isgreater than the maximum temperature difference; and selecting a fanspeed within the fan speed range based at least in part on the currentcontrol error.